1. Field of the Invention
This invention relates to transmission of electrical signals and more particularly to transmission of signals at a microwave frequency through an interface comprised of members that are relatively rotatable.
2. Description of the Prior Art
In a space communication system, for example, it may be necessary to transmit electrical signals at a microwave frequency from a stationary power source, through a single channel of what is known as an interface of relative rotation, to a rotatable antenna. When the signal is transmitted through slidable contacts, such as brushes and slip rings, the slidable contacts generate noise signals and dissipate a substantial amount of power. For this reason, slidable contacts are not desirable as the interface of relative rotation.
Preferably, the interface of relative rotation includes a coupling assembly that has noncontacting, overlapping sleeves of a length equal to one quarter of a wavelength associated with the transmitted signal. The sleeves are connected to the lines to provide a noncontacting electrical coupling therebetween. The assembly includes bearings that maintain the lines in axial alignment with one line axially rotatable with respect to the other.
The coupling assembly of the type referred to hereinbefore is described in pages 100-114 of the book, "Microwave Transmission Circuit," edited by George L. Ragen and published as Volume 9 of the Massachusetts Institute of Technology Radiation Laboratory Series. The coupling assembly and the lines comprise what is known in the art as a rotary joint.
In constructing such a rotary joint, it is desirable to make the lines with as large a diameter as possible, thereby preventing either an over heating or a breakdown of the lines when the signal is transmitted at a high power level. However, when the diameter of the lines is too large, there may be undesired modes of transmission through the rotary joint, thereby causing a substantial power loss within the lines. Additionally, power transmitted through the rotary joint may be a function of a rotational position of one of the lines relative to the other. Therefore, in the prior art there is usually a well defined limit to the diameter of the coaxial transmission lines.
It is often desirable to transmit signals from two sources through two channels of the interface of relative rotation. When a rotary joint is constructed with two channels, it is complex and, additionally, has a size that is limited for reasons similar to those given above.